A Tire Pressure Monitoring System, or TPMS, can perform real-time monitoring of a tire pressure, and provide warning for a low tire pressure or an overly high tire pressure. TPMS include direct TPMS and indirect TPMS. In indirect TPMS, tire speed changes are monitored through monitoring tire deformations (wheel rotating diameter). Then tire deformations are described by tire pressure variations. In direct TPMS, pressure sensors monitor tire pressures directly. Tire deformations are kept under their limits through tire pressures controls. The ultimate goal for direct TPMS and indirect TPMS is to monitor tire deformations and keep them under limits. Tire pressure is an intermediate variable that describes tire deformation. Based on the current TPMS standards (FMVSS 133, GB/T 26149 and et. al.), TPMS should provide the real-time tire pressure and warning by means of sound or light when real-time tire pressure is below 75% of cold tire pressure or above 125% of it.
The purpose of designing TPMS is to inform people to adjust tire pressures by providing tire pressure abnormal warning, so that crashes related to tire failure could be avoid. According to the technical report on TPMS effectiveness evaluation by NHTSA in November 2012, the presence of TPMS on a vehicle is estimated to result in a 55.6 percent reduction in the likelihood that the vehicle will have one or more severely underinflated tires (25% or more below the vehicle manufacturer's recommended cold tire pressure). However, it is difficult to evaluate the reduction of tire failure and crashes. That is to say, TPMS is not effective at preventing tire failures and crashes.